Field of the Invention
The present invention relates to an analytical cell suitable for use, e.g., in an electrode reaction analysis in analytical equipment, and a method of producing the analytical cell.
Description of the Related Art
As is well known, in an electric cell, a negative electrode active material and a positive electrode active material undergo electrode reactions in a charge-discharge process. In recent years, such electrode reactions have been analyzed during the charging/discharging process using analytical equipment. For example, an analytical cell that can be observed by a transmission electron microscope (TEM) has been proposed in In-situ Electron Microscopy of Electrical Energy Storage Materials [online], 2011, retrieved on Mar. 27, 2015 from the Internet <URL: http://energy.gov/sites/prod/files/2014/03/f11/es095_unocic_2011_o.pdf>.
This analytical cell contains a pair of substrates (silicon substrates). Each of the substrates has a rectangular observation window having a size of about 50 μm ×100 μm. The pair of substrates are partially overlapped with each other to form an overlapping portion. In the overlapping portion, the substrates are spaced from each other by a predetermined distance by a spacer interposed between the substrates. The substrates are positioned in a manner that the observation windows face each other. Further, a positive electrode active material containing LiCoO2 and a negative electrode active material containing highly oriented graphite are deposited on one of the silicon substrates by an ion beam deposition method, such that the positive electrode active material and the negative electrode active material are located between the observation windows. It should be noted that each of the negative electrode active material and the positive electrode active material is extracted from a bulk body using a focused ion beam (FIB).
The negative electrode active material and the positive electrode active material (hereinafter also referred to as active materials, collectively) are electrically connected to a negative electrode collector and a positive electrode collector (hereinafter also referred to as collectors, collectively), respectively, inside the overlapping portion. Each of the collectors extends from the inside of the overlapping portion, such that one end side thereof is exposed to the outside. Therefore, the negative electrode active material and the positive electrode active material can be electrically connected to the charging/discharging devices, etc. outside the overlapping portion through the collectors, and it is possible to cause electrode reactions, etc.
In the case of analyzing electrode reactions, etc. of the analytical cell, for example, by a holder proposed in Japanese Laid-Open Patent Publication No. 2013-535795 (PCT), the analytical cell is held in the analytical equipment, and observed using a transmission electron microscope (TEM), etc. This holder includes a holder body having a pocket accommodating the analytical cell, and a holder lid attached to the holder body for fixing the analytical cell in the pocket.
For fixing the analytical cell to the holder, firstly, among a pair of substrates of the analytical cell, one substrate that does not have any active material is placed on the bottom wall in the pocket through an O-ring. Then, another substrate having active materials is overlapped with the one substrate through the spacer, and the analytical cell is assembled in the pocket. At this time, the side wall surface of the pocket is brought into abutment against the side surfaces of the substrates to thereby position the substrates in such a manner that observation windows are overlapped with each other.
Then, for sealing the opening of the pocket accommodating the analytical cell, O-rings are interposed between the substrate of the analytical cell and the holder lid, and the holder lid is attached to the holder body. In this manner, a pressure is applied from the holder body and the holder lid to the analytical cell through the O-rings provided at both ends in the overlapping direction. As a result, the analytical cell is fixed to the holder. Further, the substrates are prevented from being shifted from the state where the substrates are positioned with respect to each other in the manner as described above.
The holder has a flow channel for electrolytic solution inside the overlapping portion, and an electrical path for connecting each of the collectors to the charge-discharge tester or the like. Therefore, by allowing the electrolytic solution to flow through the analytical cell fixed to the holder as described above via the flow channel, and connecting the electrical path to the collectors, it is possible to cause electrode reactions by the active materials. The TEM observation is carried out while transmitting an electron beam through the observation window to analyze the electrode reactions of the active materials.